[Captcha breaking] How to distinguish different captchas?

I have a set of some captcha breakers for different captchas. Some sites use those default captchas (e.g. the pligg default captcha), others not, and those I want to solve with decaptcher.

How can I know which captcha do I have? So: what could be a good fingerprint? Histogram etc, does anybody know?

isn't decaptcher cheap enough? ...for me captcha breakers doesnt matter because decaptcher nearly costs nothing

I want to use it to spam forums and wrote my own phpbb submitter because I am so tired of XRumer. 100k captchas daily though cost some money.

But what I found out just now: you can tell gocr the accuracy, so maybe gocr itself knows well if it can recognize the captcha or not?

I can offer captcha breaking service for 3,5 USD for 1000 captchas. PM.